U.S. patent application number 16/404761 was filed with the patent office on 2019-11-21 for printing apparatus and print method.
This patent application is currently assigned to MIMAKI ENGINEERING CO., LTD.. The applicant listed for this patent is MIMAKI ENGINEERING CO., LTD.. Invention is credited to Masaru Ohnishi.
Application Number | 20190351684 16/404761 |
Document ID | / |
Family ID | 66589425 |
Filed Date | 2019-11-21 |
United States Patent
Application |
20190351684 |
Kind Code |
A1 |
Ohnishi; Masaru |
November 21, 2019 |
PRINTING APPARATUS AND PRINT METHOD
Abstract
Disclosed is a printing apparatus which performs printing on a
medium in an inkjet mode. The printing apparatus includes inkjet
heads and an ultraviolet irradiation section that is an energy ray
irradiation section. In this printing apparatus, the ink is an ink
containing a solvent and generating heat in accordance with
ultraviolet rays. The ultraviolet irradiation section applies the
ultraviolet ray to the ink on the medium to evaporate at least a
portion of the solvent in the ink. When 45% by volume or more of
the solvent evaporates from an initial solvent amount, the
viscosity of the ink is 50 mPasec or more.
Inventors: |
Ohnishi; Masaru; (Nagano,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MIMAKI ENGINEERING CO., LTD. |
Nagano |
|
JP |
|
|
Assignee: |
MIMAKI ENGINEERING CO.,
LTD.
Nagano
JP
|
Family ID: |
66589425 |
Appl. No.: |
16/404761 |
Filed: |
May 7, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B41J 11/002
20130101 |
International
Class: |
B41J 11/00 20060101
B41J011/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 17, 2018 |
JP |
2018-095652 |
Claims
1. A printing apparatus which performs printing on a medium in an
inkjet mode, comprising: an inkjet head which ejects an ink to the
medium; and an energy ray irradiator which applies an energy ray,
wherein the ink is an ink containing a solvent and generating heat
in accordance with the energy ray, the energy ray irradiator
applies the energy ray to the ink on the medium to evaporate at
least a portion of the solvent in the ink, and the energy ray
irradiator applies the energy ray to the ink on the medium, so that
a viscosity of the ink is 50 mPasec or more, when 45% by volume or
more of the solvent evaporates from an initial solvent amount which
is an amount of the solvent contained in the ink at a time of
ejection from the inkjet head.
2. The printing apparatus according to claim 1, wherein the ink
contains a thickening substance which is a substance that increases
the viscosity of the ink when the amount of the solvent in the ink
decreases, and the thickening substance aggregates when the amount
of the solvent in the ink decreases to increase the viscosity of
the ink.
3. The printing apparatus according to claim 1, wherein the ink is
an ink containing latex resin particles.
4. The printing apparatus according to claim 2, wherein the ink is
an ink containing latex resin particles.
5. The printing apparatus according to claim 3, wherein when 45% by
volume or more of the solvent evaporates from the initial solvent
amount, as a distance between the latex resin particles decreases,
the viscosity of the ink increases.
6. The printing apparatus according to claim 4, wherein when 45% by
volume or more of the solvent evaporates from the initial solvent
amount, as a distance between the latex resin particles decreases,
the viscosity of the ink increases.
7. The printing apparatus according to claim 1, wherein the ink
contains a polymeric substance or an oligomer dissolved in the
solvent.
8. The printing apparatus according to claim 2, wherein the ink
contains a polymeric substance or an oligomer dissolved in the
solvent.
9. The printing apparatus according to claim 7, wherein when 45% by
volume or more of the solvent evaporates from the initial solvent
amount, an intermolecular force of the polymeric substance or
oligomer increases, and, at the same time, entanglement occurs
between molecules, so that the viscosity of the ink increases.
10. The printing apparatus according to claim 8, wherein when 45%
by volume or more of the solvent evaporates from the initial
solvent amount, an intermolecular force of the polymeric substance
or oligomer increases, and, at the same time, entanglement occurs
between molecules, so that the viscosity of the ink increases.
11. The printing apparatus according to claim 1, wherein the ink
contains a polymerizable substance which is a substance to be
polymerized by irradiation with the energy ray.
12. The printing apparatus according to claim 2, wherein the ink
contains a polymerizable substance which is a substance to be
polymerized by irradiation with the energy ray.
13. The printing apparatus according to claim 1, wherein the ink is
a colloidal ink, containing: coloring material-coated resin
particles which are particles obtained by coating a coloring
material with a resin.
14. The printing apparatus according to claim 2, wherein the ink is
a colloidal ink, containing: coloring material-coated resin
particles which are particles obtained by coating a coloring
material with a resin.
15. The printing apparatus according to claim 1, wherein the ink
comprises a cellulose fiber which is a fiber of cellulose.
16. The printing apparatus according to claim 1, wherein the energy
ray irradiator applies an ultraviolet ray as the energy ray.
17. A printing apparatus which performs printing on a medium in an
inkjet mode, comprising: an inkjet head which ejects an ink to the
medium; and an energy ray irradiator which applies an energy ray,
wherein the ink is an ink containing a solvent and generating heat
in accordance with the energy ray, the energy ray irradiator
applies the energy ray to the ink on the medium to evaporate at
least a portion of the solvent in the ink, and the ink comprises a
cellulose fiber which is a fiber of cellulose.
18. A print method which performs printing on a medium in an inkjet
mode, comprising: ejecting an ink to the medium by an inkjet head;
and applying an energy ray by an energy ray irradiator, wherein the
ink is an ink containing a solvent and generating heat in
accordance with the energy ray, the energy ray irradiator applies
the energy ray to the ink on the medium to evaporate at least a
portion of the solvent in the ink, and the ink comprises a
cellulose fiber which is a fiber of cellulose.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority benefit of Japanese
Patent Application No. 2018-095652, filed on May 17, 2018. The
entirety of the above-mentioned patent application is hereby
incorporated by reference herein and made a part of this
specification.
TECHNICAL FIELD
[0002] The present disclosure relates to a printing apparatus and a
print method.
DESCRIPTION OF THE BACKGROUND ART
[0003] Conventionally, as an ink for an ink jet printer, an
evaporation drying type ink which fixes on a medium by evaporation
of a solvent is widely used. In recent years, an ink (instantaneous
drying ink) in which the ink itself generates heat by irradiation
with energy rays such as ultraviolet rays has been proposed as an
evaporation type ink (see, for example, Patent Literature 1).
[0004] Patent Literature 1: International Publication No.
2017/135425
SUMMARY
[0005] In the conventional configuration, for example when an ink
is dried by heating a medium with a heater or the like, the ink is
indirectly heated via the medium. On the other hand, when an
instantaneous drying ink is used, the ink itself is caused to
generate heat, so that it becomes possible to directly heat the ink
while suppressing an influence of heating on the surroundings and
the like. Further, when the instantaneous drying ink is used, the
ink on a medium is irradiated with energy rays immediately after
landing on the medium, so that the ink can be efficiently dried in
a short time before smearing of the ink (such as intercolor
smearing) occurs.
[0006] However, since the configuration using the instantaneous
drying ink is a technique that has been proposed shortly, it is
desired to further study various features. Based on such
consideration, it is desired to perform printing of high quality
more appropriately. Accordingly, the present disclosure provides a
printing apparatus and a print method capable of solving the above
problems.
[0007] The inventor of this application has conducted intensive
studies on a configuration using an instantaneous drying ink. As a
result of the intensive studies, it has been found that when the
instantaneous drying ink is used, a phenomenon called a coffee
stain phenomenon may be likely to occur. The coffee stain
phenomenon is, for example, a phenomenon in which, in an ink on a
medium, a coloring material (pigment or the like) of the ink moves
to a peripheral edge having a high evaporation rate, so that the
ink fixes eccentrically to the peripheral edge during drying. In
this case, since the coloring material fixes eccentrically to the
peripheral portion, pixels formed by dots of the ink (print dots,
landing liquid droplets) have, for example, a donut shape (or ring
shape) that, while the color in the central portion is thin, the
color in the peripheral edge is thick. In this case, the dots of
the ink mean, for example, dots formed by ink droplets landing on
the medium. Further, in this case, it is conceivable that a thin
color portion is formed on a printed matter which is a printed
product, and an average density of colored color decreases. It is
also conceivable that image quality deteriorates due to these
effects.
[0008] On the other hand, the inventor of this application, through
his keen studies and researches, has found out that the reason why
the coffee stain phenomenon tends to occur is related to the
temperature of the ink during drying. More specifically, when an
instantaneous drying ink is used, the ink is irradiated with energy
rays such as ultraviolet rays to be caused to generate heat. This
also heats the ink to a high temperature to rapidly dry the ink. In
this case, the ink can be heated to a higher temperature (for
example, 80.degree. C. or higher) as compared with a case where the
ink is indirectly heated by heating a medium with a heater or the
like. However, in this case, it is conceivable that the viscosity
of the ink temporarily lowers due to elevation of the temperature
of the ink, and, for example, a flow of the ink component occurs
from the central portion to the peripheral edge within the ink dot.
As a result, it is conceivable that a coloring material of the ink
such as a pigment tends to move to the peripheral edge of the dot,
and the coffee stain phenomenon is likely to occur.
[0009] Here, in order to prevent the coffee stain phenomenon from
occurring as described above, it seems that it is sufficient to
suppress a temperature increase of the ink, for example, so as not
to lower the viscosity of the ink. However, in the case of heating
the ink while suppressing the temperature increase, ink smearing
(intercolor smearing or the like) is likely to occur due to
prolongation of the time until the ink is sufficiently dried. Thus,
only by suppressing the temperature increase of the ink, it may be
difficult to properly perform high-quality printing. Therefore, the
inventor of this application contemplated that an ink whose
viscosity rapidly increases due to evaporation of a solvent is used
without merely suppressing the temperature increase of the ink,
whereby the viscosity of the ink is prevented from lowering.
Further, the inventor of this application confirmed through tests
that the coffee stain phenomenon can be appropriately prevented by
such a method. Furthermore, the inventor of this application,
through his keen studies and researches, has found out features
necessary for obtaining the above-mentioned effects, and the
present disclosure was achieved.
[0010] In order to solve the above problems, the present disclosure
provides a printing apparatus which performs printing on a medium
in an inkjet mode. The printing apparatus includes an inkjet head
which ejects ink to the medium and an energy ray irradiator which
applies energy rays. The ink is an ink containing a solvent and
generating heat in accordance with the energy ray. The energy ray
irradiator applies the energy ray to the ink on the medium to
evaporate at least a portion of the solvent in the ink. The energy
ray irradiator applies the energy ray to the ink on the medium, so
that the viscosity of the ink is 50 mPasec or more when 45% by
volume or more of the solvent evaporates from an initial solvent
amount which is the amount of the solvent contained in the ink at
the time of ejection from the inkjet head.
[0011] With such a configuration, for example, even if the ink is
heated by irradiation with energy rays so that the temperature of
the ink becomes high, it is possible to appropriately prevent the
viscosity of the ink from becoming too low. Consequently, for
example, when the instantaneous drying ink is used, it possible to
appropriately prevent the coffee stain phenomenon. In the
conventional configuration, the coffee stain phenomenon is likely
to occur when using an ink containing a solid coloring material
such as a pigment. On the other hand, with such a configuration,
even when an ink containing a solid coloring material is used, the
coffee stain phenomenon can be appropriately prevented.
Consequently, for example, it is possible to more appropriately
perform high-quality printing. In this configuration, for example,
ultraviolet rays can be suitably used as the energy rays. In this
case, for example, a configuration using an LED (UVLED) that
generates ultraviolet rays (UVLED irradiator) or the like can be
suitably used as the energy ray irradiator.
[0012] In the case of drying the ink by irradiation with energy
rays, if a boiling point of the solvent of the ink is low, bumping
of the solvent or the like is likely to occur. When the solvent
bumps during drying of the ink, problems such as surface roughening
of the ink may occur. Thus, in this configuration, as the ink, for
example, it is preferable to use an ink in which a liquid having a
boiling point of 100.degree. C. or higher occupies 50% by weight or
more in a solvent contained in the ink at the time of ejection from
the inkjet head. With such a configuration, for example, bumping of
the solvent of the ink or the like can be made less likely to
occur. When the ink adhering to the medium is irradiated with
energy rays, it is preferable that the energy ray irradiator
irradiate the ink with energy rays such that the solvent of the ink
does not boil. With such a configuration, for example, surface
roughening of the ink or the like can be appropriately
prevented.
[0013] Here, when energy rays are applied such that the solvent of
the ink does not boil, it seems that ink smearing is likely to
occur due to a mild temperature increase of the ink. On the other
hand, according to the above configuration, by using the ink whose
viscosity rapidly increases with evaporation of the solvent, for
example even when the temperature increase of the ink is mild, it
is possible to appropriately suppress occurrence of smearing. Thus,
with such a configuration, for example, it is possible to
appropriately prevent the coffee stain phenomenon, roughening of
the ink, and smearing.
[0014] In this case, as the ink, for example, an ink containing a
thickening substance which is a substance that increases the
viscosity of the ink when the amount of the solvent in the ink
decreases may be used. In this case, for example, the thickening
substance aggregates when the amount of the solvent in the ink
decreases, thereby increasing the viscosity of the ink. With such a
configuration, by irradiating the ink with energy rays, it is
possible to rapidly and appropriately increase the viscosity of the
ink. The thickening substances can also be considered as a
substance which increases the viscosity of the ink more rapidly
than when the ink does not contain the substance.
[0015] More specifically, in this configuration, as the ink, an ink
or the like containing latex resin particles may be used. In this
case, as the latex resin particles, particles of a latex resin
dispersed in a solvent in a state in which the particle size is 30
nm to 1200 nm can be suitably used, for example. Further, in this
case, for example, the viscosity of the ink increases, as a
distance between the latex resin particles decreases in the state
in which 45% by volume or more of the solvent evaporates from the
initial solvent amount. This is considered to be due to the fact
that as the distance between the latex resin particles decreases,
for example, an attractive force and a frictional force acting
between the particles increase. With such a configuration, by
irradiating the ink with energy rays, it is possible to rapidly and
appropriately increase the viscosity of the ink.
[0016] As the ink, an ink containing a polymeric substance or an
oligomer dissolved in a solvent may be used, for example. In this
case, for example, in the state in which 45% by volume or more of
the solvent evaporates from the initial solvent amount, the
intermolecular force of the polymeric substance or oligomer
increases, and, at the same time, entanglement occurs between the
molecules, so that the viscosity of the ink increases. In this
case, the ink whose viscosity is increased changes, for example,
into a gel state. According to this configuration, by irradiating
the ink with energy rays, it is possible to rapidly and
appropriately increase the viscosity of the ink. As the ink, for
example, an ink containing a polymerizable substance which is a
substance to be polymerized by irradiation with energy rays may be
used. In this case, the polymerizable substance is, for example, a
monomer or an oligomer. Further, in this case, for example, the
viscosity of the ink increases as the polymerization reaction
occurs simultaneously with evaporation of the solvent of the ink.
According to this configuration, by irradiating the ink with energy
rays, it is possible to rapidly and appropriately increase the
viscosity of the ink.
[0017] As the ink, for example, a colloidal ink or the like may be
used. The colloidal ink contains coloring material-coated resin
particles which are particles obtained by coating a coloring
material such as a pigment with a resin such as a polymer resin.
According to this configuration, for example, by coating with a
resin, for example, even when a pigment or the like is used as a
coloring material, electrostatic repulsion between pigments can be
reduced. Also, in this case, in a way identical or similar to that
in the case of using the ink containing the latex resin particles,
for example, the viscosity of the ink increases, as a distance
between the coloring agent-coated resin particles decreases in the
state in which 45% by volume or more of the solvent evaporates from
the initial solvent amount.
[0018] As the ink, for example, an ink containing a cellulose fiber
which is a fiber of cellulose may be used. In this case, for
example, the cellulose fiber may further be contained in the ink in
each configuration described above. As the cellulose fiber, for
example, it is more preferable to use a cellulose nanofiber which
is a cellulose fiber having an average fiber length of 1 .mu.m or
less. The average fiber length of the cellulose fiber is more
preferably 700 nm or less (for example, about 50 nm to 700 nm).
With such a configuration, for example, by irradiating the ink with
energy rays, it is possible to more rapidly and appropriately
increase the viscosity of the ink. As the cellulose fiber, a
colorless and transparent one can be suitably used. With such a
configuration, for example, the cellulose fiber can be
appropriately added to the ink while suppressing the influence on
the color of the ink. For example, the cellulose fiber may be added
to the ink in a state of being coated with a resin. In this case,
the ink includes, for example, resin particles having cellulose
fibers coated with a resin such as a polymer resin.
[0019] The scope of this disclosure may include a print method
having technical features equivalent to those of the printing
apparatus described so far. Such a print method may provide similar
effects.
[0020] According to the disclosure, for example, it is possible to
more appropriately perform high-quality printing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIGS. 1A and 1B are views illustrating an example of a
printing apparatus 10 according to an embodiment of the disclosure;
FIGS. 1A and 1B are a top view and a side cross-sectional view
illustrating a simplified example of the configuration of a main
portion of the printing apparatus 10.
[0022] FIGS. 2A-2C are views and a graph for explaining a
phenomenon that occurs after a color ink has landed on a medium 50;
FIG. 2A is a view illustrating a conventional drying model; FIG. 2B
is a view illustrating a drying model of this example; FIG. 2C is a
graph comparing an ink density distribution in states illustrated
in FIGS. 2A and 2B.
[0023] FIGS. 3A and 3B are a view and a graph for explaining how to
increase viscosity in a latex ink; FIG. 3A is a view schematically
illustrating latex resin particles (Latex particles) contained in
the latex ink; FIG. 3B is a graph illustrating an example of a
difference in viscosity change due to ink.
[0024] FIGS. 4A-4C are diagrams for explaining various
modifications of ink having rapidly high viscosity evaporative
drying characteristics.
[0025] FIG. 5 is a top view illustrating a modification of the
configuration of the printing apparatus 10.
DESCRIPTION OF EMBODIMENTS
[0026] Hereinafter, embodiments of the present disclosure will be
described with reference to the drawings. FIGS. 1A and 1B
illustrate an example of a printing apparatus 10 according to an
embodiment of the disclosure. FIGS. 1A and 1B are a top view and a
side cross-sectional view illustrating a simplified example of the
configuration of a main portion of the printing apparatus 10.
Except for aspects hereinafter described, the printing apparatus 10
may be configured identically or similarly to the known printing
apparatuses. For example, the printing apparatus 10 may be further
configured identically or similarly to the known printing
apparatuses, in addition to the configurations described below.
[0027] In this embodiment, the printing apparatus 10 is an inkjet
printer that performs inkjet printing. The printing apparatus 10
includes a head portion 12, a medium supporter 14, a guide rail 16,
a scanning driver 18, a printing heater 20, a pre-heater 22, an
after-heater 24, and a controller 30. Further, the printing
apparatus 10 is a serial type inkjet printer that prompts the head
portion 12 to perform main scans. In this case, the main scan is,
for example, an operation of ejecting ink (ink droplets) while
moving in a preset main scanning direction (Y direction in the
drawing, head scanning direction). Prompting the head portion 12 to
perform main scans technically means prompting inkjet heads of the
head portion 12 to perform main scans. In this embodiment, the
printing apparatus 10 executes serial mode printing in a multi-pass
scan mode in which multiple main scans are performed at each of
positions on a medium 50 to be printed, for example.
[0028] The head portion 12 is a portion that ejects ink onto the
medium 50, and includes a carriage 100, a plurality of inkjet heads
(print heads), and an ultraviolet irradiation section 104. The
carriage 100 is a holding member that holds the inkjet heads and
the ultraviolet irradiation section 104. In this embodiment, the
inkjet heads of the head portion 12 include an inkjet head 102c, an
inkjet head 102m, an inkjet head 102y, and an inkjet head 102k
(hereinafter referred to as inkjet heads 102c to 102k) as
illustrated in the drawings. These inkjet heads are installed side
by side in the main scanning direction to be aligned in line in a
sub scanning direction (X direction in the drawing) orthogonal to
the main scanning direction.
[0029] The inkjet heads 102c to 102k are inkjet heads that eject
inks of mutually different colors and eject ink of each color of a
process color that is a basic color used for full color expression.
More specifically, the inkjet head 102c ejects cyan (C color) ink.
The inkjet head 102m ejects magenta (M color) ink. The inkjet head
102y ejects yellow (Y color) ink. The inkjet head 102k ejects black
(K color) ink. In this embodiment, as the ink of each color of
CMYK, for example, ink containing a pigment of each color of CMYK
is used. In this case, the pigment is an example of a solid
coloring material.
[0030] In this embodiment, as the ink (color ink) ejected from the
inkjet heads 102c to 102k, an evaporation drying type ink is used.
In this case, the evaporation drying type ink is, for example, an
ink which evaporates a solvent to fix on the medium 50. The solvent
is, for example, a liquid which dissolves or disperses other
components in the ink. The evaporation drying type ink can be
considered as an ink containing a solvent in an amount of 30% by
weight or more, for example. The content of the solvent in the
evaporation drying type ink is more preferably 70% by weight or
more. In this case, as the solvent, a liquid corresponding to the
type of ink is used. For example, in the case of aqueous ink, an
aqueous solvent such as water is used as a solvent. In the case of
a solvent type ink, an organic solvent is used as a solvent. The
solvent is not limited to a specific liquid, and it is conceivable
to use various liquids such as water, a liquid obtained by mixing
water with one or more solvents (organic solvents), and a liquid
obtained by mixing a plurality of solvents.
[0031] The evaporation drying type ink used as a color ink in this
embodiment is an ink (instantaneous drying ink) irradiated with an
energy ray to generate heat. The fact that the ink is irradiated
with an energy ray to generate heat is, for example, a fact that
the ink absorbs the applied energy ray to generate heat itself. In
this case, the color ink used in this embodiment can be considered
as an ink containing a solvent and generating heat in accordance
with an energy ray.
[0032] In this embodiment, ultraviolet light (UV light) is used as
the energy ray. In this case, the color ink can be considered as a
color ink (UV instantaneous drying color ink) instantaneously dried
by irradiation with ultraviolet rays. In this case, as the color
ink, for example, an ink containing an ultraviolet absorber (UV
absorber) is used. The ultraviolet absorber is an example of an
energy ray absorber that absorbs energy rays and generates heat.
The ultraviolet absorber can be considered as a substance for
heating and drying the solvent in the ink momentarily in accordance
with irradiation with ultraviolet rays. As the ultraviolet
absorber, it is preferable to use a substance (a substance that
absorbs ultraviolet rays of the emission wavelength of the
ultraviolet irradiation section 104) that appropriately absorbs
ultraviolet rays generated by the ultraviolet irradiation section
104 in the head portion 12. With such a configuration, for example,
the color ink is irradiated with ultraviolet rays to be caused to
appropriately generate heat and can function as an instantaneous
drying ink. Depending on the composition of the color ink, it is
also conceivable to use a component having an ultraviolet absorbing
action as any component of an ink vehicle (for example, coloring
material, resin, solvent, or the like). In this case, instead of
adding a dedicated ultraviolet absorber for an intended purpose of
causing the ink to generate heat, other components (for example,
coloring material, resin, solvent, or the like) in the ink may also
serve as the function of the ultraviolet absorber. The
instantaneous drying ink to be used in this embodiment can be
considered as an ink that generates heat by conversion of energy
(UV light energy) of ultraviolet rays to be applied into thermal
energy.
[0033] Further, in this embodiment, as the color ink, an ink (ink
having rapidly high viscosity evaporative drying characteristics)
whose viscosity rapidly increases as the solvent evaporates is
used. More specifically, for example, when the amount of the
solvent contained in the ink at the time of ejection from each of
the inkjet heads 102c to 102k is defined as an initial solvent
amount, by irradiation of the ink on the medium 50 with ultraviolet
rays, the viscosity of the ink reaches 50 mPasec or more once 45%
by volume or more of the solvent evaporates from the initial
solvent amount. With this configuration, for example, when the ink
is dried by irradiation with ultraviolet rays, the viscosity of the
ink can be sufficiently increased in a short time. Regarding the
ink to be used in this embodiment, the features relating to such
viscosity increase will be described in more detail later. Also,
the ink to be used in this embodiment may have features identical
or similar to those of known evaporation drying type inks, except
for points described above or to be described below. For example,
the ink to be used in this embodiment may further contain
components (such as a dispersant) identical or similar to those of
known inks.
[0034] In the head portion 12 of this embodiment, the ultraviolet
irradiation section 104 is an example of an energy ray irradiation
part and UV irradiators, and applies ultraviolet rays to color ink
adhering to the medium 50, thereby causing the color ink to
generate heat. With this configuration, for example, at least a
portion of the solvent in the ink can be evaporated by efficiently
and appropriately heating the color ink. In this embodiment, as an
ultraviolet light source in the ultraviolet irradiation section
104, for example, UVLED (UV-LED irradiators) which is an LED which
generates ultraviolet rays is used. In this case, the ultraviolet
irradiation section 104 can be considered as a UVLED irradiator.
With such a configuration, for example, it is possible to
appropriately and efficiently apply ultraviolet rays in a necessary
wavelength range. As the UVLED, UVLED having a central wavelength
of light emission of 400 nm or less can be suitably used. More
specifically, in this case, it is conceivable that the UVLED
applies ultraviolet rays having an emission center at 360 nm to 390
nm, for example, with an intensity of about 0.1 Joule/cm.sup.2 to 5
Joule/cm.sup.2. The wavelength of the ultraviolet ray generated by
the UVLED is not limited to the above-described wavelength, and may
be any wavelength as long as the instantaneous drying ink to be
used can be appropriately heated.
[0035] In this embodiment, the ultraviolet irradiation section 104
is disposed at a position behind the inkjet heads 102c to 102k
during the main scan while aligning the position in the sub
scanning direction with the inkjet heads 102c to 102k. With this
configuration, the ultraviolet irradiation section 104 applies
ultraviolet rays after the inkjet heads 102c to 102k eject the
color ink to each position to be printed on the medium 50.
Consequently, the ultraviolet irradiation section 104 causes the
color ink to generate heat and vaporizes and evaporates at least a
portion of the solvent of the color ink. With this configuration,
for example, the color ink can be efficiently dried in a short
time.
[0036] The medium supporter 14 is a table-shaped member (platen)
that supports the medium 50, and supports the medium 50 so as to
face the head portion 12. In this embodiment, the medium supporter
14 houses the print heater 20, the pre-heater 22, and the
after-heater 24 therein. The guide rail 16 is a rail member that
guides the movement of the head portion 12 during the main scanning
operation.
[0037] The scanning driver 18 is a driver that prompts the head
portion 12 to perform a scanning operation that moves relative to
the medium 50. In this case, prompting the head portion 12 to
perform the scanning operation means, for example, prompting the
inkjet heads 102c to 102k in the head portion 12 to perform the
scanning operation. In this embodiment, the scanning driver 18
prompts the head portion 12 to perform main scans and sub scans as
the scanning operation. In this case, the scanning driver 18
prompts the head portion 12 to perform the main scan, thereby
prompting the inkjet heads 102c to 102k to eject color ink to each
position of the medium 50. In addition, the ultraviolet irradiation
section 104 is moved together with the inkjet heads 102c to 102k
during the main scan, whereby ultraviolet rays are applied to the
color ink on the medium 50. In this example, the printing apparatus
10 is a unidirectional printer that performs only main scan in one
direction (unidirection) indicated by an arrow as a moving
direction during printing in the drawing. The scanning driver 18
prompts the head portion 12 to perform sub scan in the intervals
between main scans (every pass scan) to sequentially change the
position of the medium 50 that faces the head portion 12. In this
case, the sub scan refers to, for example, an operation of moving
relative to the medium 50 in the sub scanning direction orthogonal
to the main scanning direction. More specifically, in this
embodiment, the scanning driver 18 conveys the medium 50 in a
conveyance direction parallel to the direction indicated as the X
direction in the drawing, thereby prompting the head portion 12 to
perform sub scan. In this case, the medium 50 is conveyed in the
conveyance direction (medium conveyance direction) indicated by an
arrow in the drawing by using a roller or the like not illustrated,
for example.
[0038] The print heater 20, the pre-heater 22, and the after-heater
24 are heaters for heating the medium 50. Among them, the print
heater 20 is a heater for heating the medium 50 at a position
facing the head portion 12 (a position below the head portion 12).
By using the print heater 20, for example, it becomes possible to
more efficiently heat the ink on the medium 50. In this case, the
configuration of the printing apparatus 10 of this embodiment can
also be considered as a configuration in which the ink is dried
using the ultraviolet irradiation section 104 and the print heater
20 together.
[0039] Here, when the heating temperature in the print heater 20 is
high, for example, the inkjet head in the head portion 12 is
heated, so that problems such as nozzle clogging are likely to
occur. In this case, the nozzle clogging means, for example, that
the nozzle of the inkjet head is clogged by drying of ink. Thus,
the heating temperature by the print heater 20 is preferably set to
70.degree. C. or lower. In this embodiment, as described above, it
is possible to efficiently heat ink using the ultraviolet
irradiation section 104. Thus, it is more preferable that the
heating temperature by the print heater 20 be set to a sufficiently
low temperature for the purpose of suppressing the influence of
environmental temperature, making the temperature of the medium 50
constant, and the like. Also in this case, by using the print
heater 20, the evaporation condition of the solvent in the ink can
be appropriately fixed. More specifically, for example, the print
heater 20 heats a region facing the print heater 20 at a
temperature closer to the room temperature (for example, about
50.degree. C. or lower, more specifically, for example, about
30.degree. C. to 50.degree. C.). The heating temperature of the
medium 50 by the print heater 20 is preferably 40.degree. C. or
less, more preferably 35.degree. C. or less. With this
configuration, for example, the influence of environmental
temperature and the like can be appropriately suppressed while
suppressing problems such as nozzle clogging.
[0040] The pre-heater 22 is a heater that heats (preheats) the
medium 50 on the upstream side of the head portion 12 in the
conveyance direction. By using the pre-heater 22, for example, the
initial temperature of the medium 50 can be appropriately adjusted
before reaching the position of the head portion 12. In this case,
the heating temperature of the medium 50 by the pre-heater 22 is
also preferably set to a sufficiently low temperature (for example,
50.degree. C. or lower, preferably 40.degree. C. or lower, more
preferably 35.degree. C. or lower) for the purpose of, for example,
suppressing the influence of environmental temperature. The
after-heater 24 is a heater that heats the medium 50 on the
downstream side of the head portion 12 in the conveyance direction.
By using the after-heater 24, for example, it is possible to more
reliably dry the ink and to prevent the solvent from remaining
before the printing is completed. Further, by using the
after-heater 24, for example, it is possible to enhance the
adhesion of the ink to the medium 50. It is conceivable that the
heating temperature of the medium 50 by the after-heater 24 is set
to, for example, about 30.degree. C. to 50.degree. C. The
after-heater 24 can be considered as, for example, a heater for
post-heating (post-dryers), and the like for completely removing
residual solvent components at the time of heating by the print
heater 20. The heating temperature of the after-heater 24 may be
set to a high temperature of a certain extent in a range lower than
or equal to a heatproof temperature of the medium 50 to be
used.
[0041] As described above, in this embodiment, at least a portion
of the solvent in the ink is evaporated using the ultraviolet
irradiation section 104. In this case, the ink can be dried mainly
by irradiation with ultraviolet rays. Thus, some or all of the
print heater 20, the pre-heater 22, and the after-heater 24 may be
omitted depending on the environment of using the printing
apparatus 10 and the desired quality of printing. As the print
heater 20, the pre-heater 22, and the after-heater 24, various
known heaters may be used. More specifically, as the print heater
20, the pre-heater 22, and the after-heater 24, for example,
various heaters, hot air blowers, and the like (for example, a heat
transfer heater, a warm air heater, an infrared light heater, and
the like) can be suitably used. Further, as the after-heater 24,
for example, an ultraviolet light source (UV light irradiators) may
be used.
[0042] The controller 30 is, for example, a CPU of the printing
apparatus 10, and controls the operation of each portion of the
printing apparatus 10. For example, during each main scan, the
controller 30 prompts the inkjet heads 102c to 102k to eject ink at
timings set according to images to be printed. According to this
embodiment, for example, a desired image can be appropriately
printed using the instantaneous drying ink.
[0043] Subsequently, the features of the printing operation
performed in this embodiment will be described in more detail.
FIGS. 2A-2C are views and a graph for explaining a phenomenon that
occurs after a color ink has landed on the medium 50. FIG. 2A is a
view illustrating an example (conventional dry model) of how to dry
the ink when using an instantaneous drying ink having a
conventional configuration, and illustrates an example of a state
of a dot formed by the color ink. FIG. 2B is a view illustrating an
example (dry model of this embodiment) of how to dry the ink when
using the instantaneous drying ink of this embodiment, and
illustrates an example of a state of a dot formed by the color ink.
For the sake of convenience of illustration, in FIGS. 2A and 2B,
differences in color strength are schematically indicated by
shading patterns. FIG. 2C is a graph comparing an ink density
distribution (density distribution after drying) in a state
illustrated in FIGS. 2A and 2B.
[0044] As described above, in this embodiment, an instantaneous
drying color ink or the like is used, and the ink is dried by
irradiation with ultraviolet rays. In this case, unlike the case
where the ink is indirectly heated by heating the medium with a
heater or the like, for example, the ink is directly heated by
irradiation with ultraviolet rays, so that, for example, it is
possible to efficiently and appropriately heat the ink while
suppressing the influence on the surrounding configuration and the
medium 50. Consequently, the ink can be heated to a higher
temperature, for example, as compared with the case where the ink
is heated using only a heater.
[0045] However, in this case, if only an instantaneous drying color
ink having a conventional configuration is used, it is conceivable
that, as the temperature of the ink increases, the viscosity of the
ink temporarily lowers, and, as indicated by an arrow in FIG. 2A,
for example, a flow of the ink component occurs from the central
portion to the peripheral edge within dots of the ink formed by ink
droplets landing on the medium. In this case, the use of
instantaneous drying color ink having a conventional configuration
means, for example, the use of instantaneous drying color ink which
does not have the feature that the viscosity rapidly increases with
the evaporation of the solvent as described above. Such a
phenomenon can be considered as a phenomenon in which a coloring
material of the ink such as a pigment tends to move to the
peripheral edge of the dot due to temporarily lowering of the
viscosity of the ink occurring during drying of the ink, and the
coffee stain phenomenon is likely to occur. More specifically, in
this case, for example, as illustrated in FIG. 2A, in a color
density distribution (density distribution after drying) in the ink
dot, the color is thin near the center and is dark at the
peripheral portion. In this case, deterioration of image quality
may occur due to influences such as occurrence of a thin portion of
color of an image to be printed and a decrease of an average
density of colored color. In addition, in this case, the color
density distribution within the ink dot (density distribution
within the dot) becomes like a curve shown by the broken line
marked with reference letter A in FIG. 2C, for example. In this
case, only the peripheral edge of the ink dot becomes high density,
and in the center portion of the dot, a low density state in which
the color is almost the background color of the medium 50 is
obtained. As a result, for example, the coloring area ratio in the
image may decrease, and the image may become thin.
[0046] On the other hand, in the case of using an instantaneous
drying ink having such a feature that the viscosity increases
rapidly with evaporation of the solvent as in this embodiment,
immediately after landing of the color ink, the viscosity of the
ink can be appropriately increased. In this case, even if the
temperature of the color ink becomes high by irradiation with
ultraviolet rays, since the viscosity of the color ink rapidly
increases so as to prevent movement of the coloring material in the
ink as well as evaporation of the solvent due to a temperature
increase, the phenomenon in which the coloring material moves to
the peripheral edge of the dot hardly occurs. More specifically, in
this case, the viscosity of the color ink increases in a short
time, so that it is possible to make lowering of the viscosity
unlikely to occur in the process of evaporating and drying the
color ink by irradiation with ultraviolet rays (during heat
generation of the color ink). Consequently, for example, movement
(movement in the evaporation and drying process) of the coloring
material (such as particles of the pigment) in the ink occurring
when the viscosity of the ink is low can be made unlikely to occur.
Thus, according to this embodiment, for example, it is possible to
appropriately prevent non-evaporating components (such as pigments)
from gathering at the peripheral edge of the ink dot. Consequently,
for example, it possible to properly prevent the occurrence of the
coffee stain phenomenon, and the density of the ink dot can be
appropriately increased to the center portion. In addition, in this
case, the color density distribution within the ink dot becomes
like a curve shown by the solid line marked with reference letter B
in FIG. 2C, for example. In this case, as is apparent from the
comparison with the curve marked with reference letter A, it is
possible to appropriately realize a uniform density distribution up
to the inside of the ink dot. Consequently, it is possible to
appropriately increase the average density of a printed matter and
to perform high-quality printing.
[0047] Subsequently, with respect to the ink used in this
embodiment, the feature that the viscosity rapidly increases with
evaporation of the solvent will be described in more detail. As
described above, the viscosity of the ink to be used in this
embodiment is 50 mPasec or more once 45% by volume or more of the
solvent evaporates from the initial solvent amount by irradiation
with ultraviolet rays. Once 45% by volume or more of the solvent
evaporates from the initial solvent amount, the viscosity of the
ink is preferably 100 mPasec or more, more preferably 500 mPasec or
more. By using the ink having such features, it is possible to
appropriately prevent the occurrence of the coffee stain phenomenon
as described above.
[0048] More specifically, in this embodiment, as the ink, a latex
ink (Latex ink) or the like having the above features can be
suitably used. In this case, the use of the latex ink means the use
of a latex ink (instantaneous drying latex ink) which generates
heat by irradiation with ultraviolet rays. Unless otherwise
specified, as various inks described above or to be described
below, an ink (instantaneous drying ink) having a property of
generating heat by irradiation with ultraviolet rays is used. Latex
is, for example, a system in which fine particles of a polymer are
dispersed in a stable state in a solvent such as water, for
example. The latex ink is an ink containing components in the state
of such a system. Further, the latex ink can be considered as an
ink containing latex resin particles (Latex particles). In this
case, as the latex resin particles, particles of a latex resin (for
example, particles of a synthetic latex resin) dispersed in a
solvent in a state in which the particle size is 30 nm to 1200 nm
can be suitably used, for example. In this case, the particle size
of the latex resin particles is, for example, a particle size
(diameter) in design. When the particle size of the latex resin
particles is 30 nm to 1200 nm, for example, among the latex resin
particles contained in the ink, the particle size of the latex
resin particles at a ratio of 70% (70% by weight) or more by weight
is within this range. This ratio is preferably 80% or more, more
preferably 90% or more.
[0049] In this case, in the state in which 45% by volume or more of
the solvent evaporates from the initial solvent amount, for
example, as the latex resin particles approach each other and the
distance between the particles decreases, the viscosity of the ink
rapidly increases. This is considered to be due to the fact that as
the distance between the latex resin particles decreases, for
example, an attractive force and a frictional force acting between
the particles increase. In this case, for example, it is
conceivable that, even when dispersants existing so as to surround
the latex resin particles in the latex resin particles approach
each other, the influence of increase in an inter-particle force
and friction increases, and the viscosity of the ink increases.
Thus, according to this embodiment, for example, by irradiating the
ink with ultraviolet rays, it is possible to rapidly and
appropriately increase the viscosity of the ink.
[0050] In the case of using the latex ink, it is conceivable that
the rapid increase in viscosity as described above is caused by
aggregation of components dispersed in the solvent. Thus, in the
case of using the latex ink, the feature that the viscosity
increases as described above can be considered as a feature that
components dispersed in the solvent aggregate once 45% by volume or
more of the solvent evaporates from the initial solvent amount. In
this case, the component dispersed in the solvent means, for
example, a component (for example, latex resin particles or the
like) in which the amount of the solvent is dispersed in the
solvent at the time of the initial solvent amount.
[0051] As to how to increase the viscosity in the latex ink, as
described below with reference to FIGS. 3A and 3B, for example, it
can be considered that viscosity increase with respect to
evaporation of the solvent is faster than solvent ink or the like.
FIGS. 3A and 3B are a view and a graph for explaining how to
increase the viscosity in the latex ink. FIG. 3A is a view
schematically illustrating latex resin particles (Latex particles)
contained in the latex ink; FIG. 3B is a graph illustrating an
example of a difference in viscosity change due to ink, and
illustrates an example of a change in ink viscosity with a decrease
in solvent due to evaporation for a latex ink and a solvent
ink.
[0052] Here, in FIG. 3B, for the sake of convenience of
illustration, a reduction amount of the solvent of the ink is
illustrated by a relationship between the viscosity and an ink
weight reduction rate and a reduction rate in weight ratio (ink
weight reduction rate) as illustrated in the drawing. However, in
this case as well, in terms of the volume ratio, the viscosity of
the latex ink is 50 mPasec or more once 45% by volume or more of
the solvent evaporates from the initial solvent amount. In this
embodiment, it can be considered that spherical resin particles are
dispersed in the latex ink as illustrated in FIG. 3A, for example.
In this case, when the amount of the solvent decreases by about 40%
by weight (wt %) from the initial amount due to evaporation of the
solvent, the viscosity of the latex ink increases to about 100
mPasec or more (at least 50 mPasec or more). Further, in this case,
considering the volume ratio, it is conceivable that the viscosity
of the ink increases to about 100 mPasec or more (at least 50
mPasec or more) once 45% by volume or more of the solvent
evaporates from the initial solvent amount. In this case, it can be
considered that the latex ink satisfies, for example, the condition
as a rapidly high viscosity ink. Thus, in this case, for example,
even if the ink is heated by irradiation with ultraviolet rays so
that the temperature of the ink becomes high, it is possible to
appropriately prevent the viscosity of the ink from becoming too
low. This also makes it possible, for example, to stop flowing and
smearing of the ink at the initial stage of drying the ink and to
effectively suppress the coffee stain phenomenon and the like.
[0053] On the other hand, as illustrated in contrast with the
characteristics of the latex ink in FIG. 3B, in the case of using
the solvent ink, even if the solvent of the ink decreases, the
viscosity of the ink increases much more slowly than in the case of
the latex ink. More specifically, for example, once the amount of
the solvent decreases by about 40% by weight (wt %) from the
initial amount due to evaporation of the solvent, the viscosity of
the solvent ink is still about 10 mPasec or less.
[0054] Here, as also described above, in the latex ink, the latex
resin particles are dispersed in the solvent of the ink. In this
case, when the amount of the solvent decreases, the distance
between the particles decreases, so that the components dispersed
in the solvent aggregate, and the viscosity of the ink increases
rapidly. On the other hand, in the case of the solvent ink,
components such as a resin (binder resin) are not dispersed but
dissolved in a solvent used as the solvent. In this case, even if
the amount of the solvent decreases, aggregation or the like as in
the case of the latex ink does not occur. As a result, it is
conceivable that the viscosity increase in the case of the solvent
ink is slower than in the case of the latex ink. As can be seen
from the drawing, also in the case of the solvent ink, the
viscosity increases greatly once the amount of the solvent
decreases by about 80% by weight (wt %) from the initial amount.
This is probably because components (binder resin and the like)
dissolved in the solvent are not completely dissolved due to
extremely small amount of the solvent.
[0055] As described above, in the case of using the latex ink, it
can be conceivable that the above-described viscosity rapid
increase occurs because the latex resin particles are dispersed in
the solvent. In this case, the latex resin particles can be
considered as, for example, an example of thickening substances.
The thickening substance is, for example, a substance which
increases the viscosity of the ink when the amount of the solvent
in the ink decreases. The thickening substances can also be
considered as a substance which increases the viscosity of the ink
more rapidly than when the ink does not contain the substance. In
the modification of the ink used in this embodiment, an ink other
than the latex ink may be used as the ink whose viscosity increases
rapidly as described above. Also in this case, an ink containing
some thickening substance may be used.
[0056] Depending on properties of the thickening substance, it is
not necessarily a substance which is dispersed in a solvent, but a
substance which dissolves in a solvent or the like may be used. For
example, when a substance having a sufficiently large molecular
weight is used, even when the thickening substance is dissolved in
the solvent, it is possible to rapidly increase the viscosity of
the ink when the solvent is reduced. More specifically, in this
case, for example, an ink containing a polymeric substance or an
oligomer dissolved in a solvent may be used. In this case, the
polymeric substance or oligomer can be considered as an example of
thickening substances. In this case, for example, by using a
polymeric substance or an oligomer having a sufficiently large
molecular weight, once evaporation of the solvent of the ink
progresses (for example, once 45% by volume or more of the solvent
evaporates from the initial solvent amount), it is possible to
appropriately increase the intermolecular force (for example, force
between molecular chains) of the polymeric substance or oligomer.
Further, in this case, in addition to the increase in the
intermolecular force, entanglement between molecules (for example,
entanglement between molecular chains) may occur. In this case, for
example, the ink changes into a gel state, and the viscosity
increases rapidly. Thus, according to this configuration, for
example, by irradiating the ink with ultraviolet rays, it is
possible to rapidly and appropriately increase the viscosity of the
ink.
[0057] As an ink (ink having rapidly high viscosity evaporative
drying characteristics) whose viscosity rapidly increases as
described above, in addition to the above-described ink, various
inks may be used. FIGS. 4A-4C are diagrams for explaining various
modifications of ink having rapidly high viscosity evaporative
drying characteristics.
[0058] First, the modification illustrated in FIG. 4A will be
described. In this modification, as the ink, the colloidal ink is
used. The colloidal ink contains coloring material-coated resin
particles which are particles obtained by coating a coloring
material with a resin such as a polymer resin. As a coloring
material, a pigment may be used, for example. In this case, for
example, the coloring agent-coated resin particles can be
considered as capsule type coloring material particles in which
individual pigment particles or a plurality of pigment particles
are coated with a polymer resin in order to reduce electrostatic
repulsion between the pigments. In this modification, the coloring
agent-coated resin particles are dispersed in a solvent. When the
amount of the solvent is reduced due to evaporation of the solvent,
the distance between the coloring agent-coated resin particles
decreases, for example, so that the viscosity of the ink rapidly
increases in a way identical or similar to that in the case of the
latex ink described above. Thus, in this modification, the coloring
agent-coated resin particles can be considered as an example of
thickening substances.
[0059] Here, the ink of this modification can be considered as an
instantaneous drying ink (the next generation ink of an
instantaneous drying type) obtained by adding, for example, an
ultraviolet absorber to the ink (hereinafter referred to as the
next generation ink) described as the ink of the present disclosure
or the like in Japanese Unexamined Patent Publication No.
2013-241565. In this case, for example, by adjusting the amount of
the coloring agent-coated resin particles or the dispersant to be
added, it is possible to appropriately realize the ink whose
viscosity rapidly increases as described above. Other than the
above-described matters, the ink of this modification may have
features identical or similar to the next generation ink disclosed
in Japanese Unexamined Patent Publication No. 2013-241565. In the
above description, for convenience of explanation, the ink of this
modification is distinguished from the latex ink. However, the ink
of this modification can also be considered as an ink (for example,
a special latex ink) having the features of the latex ink.
[0060] Subsequently, the modifications and the like illustrated in
FIGS. 4B and 4C will be described. In the above description, a
thickening substance for rapidly increasing the viscosity of the
ink has been described, mainly in the case of using a resin.
However, as a thickening substance, a substance other than a resin
may be used. As such a thickening substance, for example, a
cellulose fiber which is a fiber of cellulose may be used. Such an
ink can be considered as an instantaneous drying ink including
cellulose fibers. In this case, if the solvent in the ink decreases
due to evaporation, a distance between the cellulose fibers
decreases, and the intermolecular force increases. In addition, the
viscosity of the ink rapidly increases due to entanglement or the
like.
[0061] As the cellulose fiber, for example, it is more preferable
to use a cellulose nanofiber which is a cellulose fiber having an
average fiber length of 1 .mu.m or less. The average fiber length
of the cellulose fiber is more preferably 700 nm or less (for
example, about 50 nm to 700 nm). With such a configuration, for
example, by irradiating the ink with ultraviolet rays, it is
possible to more rapidly and appropriately increase the viscosity
of the ink. As the cellulose fiber, a colorless and transparent one
can be suitably used. With such a configuration, for example, the
cellulose fiber can be appropriately added to the ink while
suppressing the influence on the color of the ink.
[0062] As illustrated in FIG. 4B, for example, the cellulose fiber
may be added to the ink in a state of being coated with a resin. In
this case, the ink includes, for example, resin particles having
cellulose fibers coated with a resin such as a polymer resin. With
such a configuration, for example, it is possible to appropriately
prevent occurrence of deviation of the cellulose fiber in the
solvent. As compared with the case of directly adding the cellulose
fiber, for example, an influence on ejection operation and the like
can be made unlikely to occur. Thus, according to this
modification, when the cellulose fiber is used as the thickening
substance, the cellulose fiber can be added more appropriately.
Depending on the required features of the ink and the like, the
cellulose fiber may be added directly to the ink. In this case, the
cellulose fiber is contained in the ink in a state of being
directly dispersed in a solvent, for example.
[0063] In a further modification of the ink, a cellulose fiber may
be further added to an ink containing a thickening substance other
than the cellulose fiber. In this case, the cellulose fiber may be
added to a latex ink of an instantaneous drying type, for example.
For example, the cellulose fiber may be added to the next
generation ink of an instantaneous drying type. When the cellulose
fiber is added to the next generation ink of an instantaneous
drying type, as illustrated in FIG. 4C, for example, the cellulose
fiber may be further covered with a resin (coloring agent-coated
resin particles) covering a coloring material. With this
configuration, it is possible to properly add the cellulose fiber
by taking advantage of the features of the next generation ink.
[0064] In the above description, the method of rapidly increasing
the viscosity of the ink has been described, and the method (that
is, a physical method) in which a physical force such as an
intermolecular force acts on a substance functioning as a
thickening substance to increase the viscosity has been mainly
described. However, in a further modification of the ink, the
viscosity of the ink may be increased by a chemical method that
causes a chemical reaction to occur in a substance functioning as a
thickening substance. More specifically, in this case, for example,
an ink containing a polymerizable substance which is a substance to
be polymerized by irradiation with energy rays such as ultraviolet
rays may be used. In this case, as the polymerizable substance, for
example, a monomer or oligomer of a resin (UV curable resin) which
is cured by irradiation with ultraviolet rays may be used. In this
case, such a polymerizable substance can be considered as a
thickening substance. Further, in this case, the polymerizable
substance is dissolved in the solvent of the ink, for example,
initiates a polymerization reaction in response to irradiation with
ultraviolet rays, and is polymerized. Consequently, the viscosity
of the ink is rapidly increased Also in this case, the
instantaneous drying ink may be used as the ink. In this case, the
viscosity of the ink increases as the polymerization reaction
occurs simultaneously with evaporation of the solvent of the ink.
According to this configuration, for example, by irradiating the
ink with energy rays, it is possible to rapidly and appropriately
increase the viscosity of the ink. In this case, the ink may
contain, for example, a substance which also serves as a
polymerization initiator as an ultraviolet absorber which absorbs
ultraviolet rays to generate heat. As the polymerization initiator,
a substance different from the ultraviolet absorber for heating the
ink may be added.
[0065] As described above, inks of various configurations may be
used as the ink having rapidly high viscosity evaporative drying
characteristics. In this case, the specific configuration and the
like of the printing apparatus 10 using the ink having rapidly high
viscosity evaporative drying characteristics are not limited to the
above-described configuration, and various modifications can be
made. FIG. 5 is a top view illustrating a modification of the
configuration of the printing apparatus 10. In FIG. 5, components
denoted by the same reference symbols as those of FIGS. 1A and 1B
have features identical or similar to those of the components of
FIGS. 1A and 1B, except for points to be described below.
[0066] In this modification, the printing apparatus 10 performs
printing by further using white ink. In this case, the white ink is
an example of a special color ink. More specifically, the head
portion 12 of this modification further includes an inkjet head
102w for white ink, in addition to the inkjet heads 102c to 102k
for process color. As illustrated in the drawing, the inkjet head
102w is disposed so as to form different rows so as to be shifted
in position in the sub scanning direction from the inkjet heads
102c to 102k. With such a configuration, for example, it is
possible to properly perform undercoating and overcoating using a
white ink. In accordance with such an arrangement of the inkjet
heads, in this modification, the head portion 12 has the
ultraviolet irradiation sections 104. One of the ultraviolet
irradiation sections 104 is disposed at a position behind the
inkjet heads 102c to 102k in the moving direction of the head
portion 12 during the main scan while aligning the position in the
sub scanning direction with the inkjet heads 102c to 102k, in a way
identical or similar to the ultraviolet irradiation section 104 in
FIGS. 1A and 1B. Another one of the ultraviolet irradiation
sections 104 is disposed at a position behind the inkjet head 102w
in the moving direction of the head portion 12 during the main scan
while aligning the position in the sub scanning direction with the
inkjet head 102w.
[0067] In this modification, an ink having rapidly high viscosity
evaporative drying characteristics is used as while ink and the
inks of CMYK. Thus, also in this modification, it is possible to
obtain the same effect as in the case described above with
reference to FIGS. 1A-4C. Further, in a further modification of the
configuration of the printing apparatus 10, for example, the inkjet
heads 102c to 102k for process color may be arranged in different
rows so as to be shifted in position in the sub scanning direction
for each color. In the above description, for the configuration of
the printing apparatus 10, an example of the configuration in the
case of performing main scan in unidirection (unidirectional
printing) has been described mainly. However, in a further
modification of the configuration of the printing apparatus 10, a
configuration that performs a reciprocating main scan
(bi-directional printing) may be used as the configuration of the
printing apparatus 10. In this case, it is preferable that the
ultraviolet irradiation section 104 be disposed not only on one
side but on both sides in the main scanning direction with respect
to the corresponding inkjet head. The configuration of the printing
apparatus 10 is not limited to the serial type configuration, but a
line type configuration (line printer) may be used. In this case,
the line type configuration is, for example, a configuration in
which ink is ejected from the inkjet head while conveying the
medium in a predetermined direction without moving the position of
the inkjet head. Also in these cases, by using the ink having
rapidly high viscosity evaporative drying characteristics, for
example, the occurrence of the coffee stain phenomenon and the like
is prevented, and high-quality printing can be appropriately
performed.
[0068] Next, a supplementary explanation related to the respective
configurations described above will be made, and further
modifications will be described. First, the effects and the like
obtained by the respective configurations described above will be
described again. For convenience of explanation, in the following
description, the configurations described above are collectively
referred to as this embodiment.
[0069] As also described above, in this embodiment, the
instantaneous drying ink is used, and printing is performed by a
method (UV instantaneous drying method) of instantaneously drying
ink by irradiation with ultraviolet rays. In this case, the ink is
instantaneously fixed on the medium to suppress occurrence of
smearing, and high-speed printing can be performed. In general, as
the instantaneous drying ink, for example, an ink prepared by
adding an ultraviolet absorber to various known evaporation drying
type inks can be used. As known evaporation drying type inks, for
example, known solvent inks, aqueous inks, latex inks, other
emulsion type inks, and the like can be used. In this case, by
using the instantaneous drying ink, for example, even in the case
of using a medium on which it is difficult to perform printing
directly due to smearing or the like in an ordinary instantaneous
drying ink, printing directly on the medium can be appropriately
performed. For example, when an aqueous ink of an instantaneous
drying type is used, printing can be appropriately performed on an
absorbent medium such as paper or cloth or non-absorbent medium
such as various plastic films, metals, and glasses. In this case,
high resolution and high image quality printing can be
appropriately performed, for example, by appropriately suppressing
occurrence of smearing.
[0070] More specifically, in the case of using the instantaneous
drying ink, for example, even when printing is performed at high
speed while reducing the number of printing passes, it is possible
to appropriately prevent occurrence of smearing. Thus, for example,
it is possible to appropriately realize a high-speed printer which
performs printing at high speed. As the printing apparatus 10, it
is possible to use the printing apparatuses 10 of various
configurations from a one-pass method to a multipass method
(multipass printing). By appropriately preventing occurrence of
smearing, it is also possible to realize a media free configuration
using various media, for example. Consequently, as described above,
for example, even in the case of using a medium or the like which
has been unable to be used due to exacerbation of the problem of
smearing in the conventional evaporation drying type ink, it is
possible to eject ink directly thereto and to perform high
definition printing. In this case, as the medium, for example,
various media such as a medium in which a receptor layer is not
formed, an absorbent (permeable) medium, and a non-absorbent
(impermeable) medium can be widely used.
[0071] In the case of using the instantaneous drying ink, the ink
can be directly and efficiently heated as compared with a
configuration in which the ink is indirectly heated via a medium
using a heater or the like. As in each configuration described
above, when ultraviolet rays are used as energy rays, for example,
the ultraviolet rays can penetrate into the interior of the ink
adhering to the medium to heat the ink from the interior. Thus, for
example, even when a film is formed on the surface of the ink
during drying of the ink, it is possible to more appropriately dry
the ink at a portion surrounded by the film. In the case of using
the instantaneous drying ink, it is possible to realize, for
example, miniaturization and cost reduction of the apparatus and
power saving, as compared with the case of using a heater. More
specifically, in the case of using the instantaneous drying ink,
for example, the configuration for heat dissipation can be
simplified, whereby the size and cost of the apparatus can be
reduced, as compared with the case of using a heater. In addition,
the power saving can be realized so that the average power
consumption is about not more than a few tenths and the standby
power is zero.
[0072] As described above, in this embodiment, instead of mere
instantaneous drying ink, the ink having rapidly high viscosity
evaporative drying characteristics whose viscosity rapidly
increases with evaporation of the solvent is used. In this case, as
described above, it is possible to appropriately suppress
occurrence of the coffee stain phenomenon and to appropriately
perform high-quality printing. In addition, the viscosity of the
ink is increased in a short time, and the occurrence of the coffee
stain phenomenon is appropriately suppressed, so that, for example,
it is also possible to appropriately obtain a printing result with
high density and without bleeding.
[0073] Here, as a method of suppressing ink smearing, there are
conventionally known a method in which a flocculant (or coagulant)
for flocculating (or coagulating) the ink, or the like is ejected
to a medium in advance, and then printing with color ink is
performed. In this case, by flocculating (or coagulating) the ink,
it is also conceivable that the coffee stain phenomenon can be
prevented even when an ink containing a pigment or the like is used
as a coloring material, for example. However, in the case of using
printing by such a method, for example, when an absorbent paper or
cloth made of fibers is used as a medium, a large amount of liquid
is absorbed by the medium, so that problems of curling and cockling
of the medium tend to occur. As a result, meandering of the
conveyed medium, contact between the inkjet head and the medium,
and the like occur, which may cause a problem of quality
deterioration (impairment of image quality) of an image to be
printed. Curling, cockling, and the like are particularly likely to
occur, for example when double-sided printing is performed on a
medium. On the other hand, according to this embodiment, ink
smearing and the coffee stain phenomenon can appropriately be
prevented without using a flocculant or the like. This also makes
it possible to prevent curling, cockling, and the like from
occurring even when using an absorbent medium, for example.
[0074] In this embodiment, since the viscosity of the ink can be
increased in a short time, it is possible to appropriately prevent
smearing even when the ink is irradiated with ultraviolet rays
under milder conditions, for example. In this case, for example,
bumping of ink can be prevented by irradiating the ink with
ultraviolet rays under mild conditions. Consequently, for example,
surface roughening of the ink or the like can be appropriately
prevented.
[0075] In this case, for example, even when the boiling point of
the solvent is low, the occurrence of smearing can be appropriately
suppressed by increasing the viscosity of the ink in a short time.
Consequently, surface roughening of the ink or the like can be more
appropriately prevented. More specifically, in the case of drying
the ink by irradiation with ultraviolet rays, if the boiling point
of the solvent of the ink is low, irradiation energy of ultraviolet
rays becomes excessive, for example, only by irradiation with
ultraviolet rays in a short time, so that bumping of the solvent is
likely to occur. When the solvent bumps during drying of the ink,
the ink surface becomes a porous film, so that problems such as
surface roughening are likely to occur. As a result, it becomes
difficult to perform high-gross printing. Even if it does not reach
the bumping phenomenon, for example, in a case where printing is
performed on an impermeable medium such as plastic with an ink
having a low boiling point of the solvent, if ultraviolet rays are
applied immediately after landing, the ink is dried before the
surface of the ink is sufficiently flattened, so that the surface
tends to be matte. Thus, also in such a case, it becomes difficult
to perform high-gross printing.
[0076] Thus, in this embodiment, as the ink, for example, it is
preferable to use an ink in which a liquid having a boiling point
of 100.degree. C. or higher occupies 50% by weight or more in a
solvent contained in the ink at the time of ejection from the
inkjet head. With such a configuration, for example, bumping of the
solvent of the ink or the like can be made less likely to occur. In
this case, for example, ultraviolet rays may be applied under the
condition that the ink on the medium does not boil, and the ink may
be dried. With such a configuration, for example, surface
roughening of the ink or the like can be appropriately prevented.
For example, even when an impermeable medium such as plastic is
used, the surface of the ink can be appropriately flattened by
drying the ink over a certain period of time.
[0077] When ultraviolet rays are applied such that the solvent of
the ink does not boil, it seems that ink smearing tends to occur
due to a mild temperature increase of the ink. However, in this
embodiment, as described above, the ink whose viscosity rapidly
increases with evaporation of the solvent is used. In this case,
even when the temperature increase of the ink is mild, it is
possible to appropriately suppress occurrence of smearing. From a
viewpoint other than the above-mentioned viewpoints, a maximum
supplied energy of ultraviolet rays applied to the ink on the
medium may be set within a range in which burning does not occur in
the ink or the like, for example. In this case, the maximum
supplied energy is, for example, the maximum value of the energy of
the applied ultraviolet rays. In this case, the energy of the
applied ultraviolet rays (the energy corresponding to a cumulative
light quantity) depends on the irradiation intensity and
irradiation time of the ultraviolet irradiation section 104 (see
FIGS. 1A and 1B). It is conceivable that the irradiation time
varies according to printing conditions such as the printing speed,
the number of printing passes, and printing dot density. Thus, it
is preferable that the maximum supplied energy be appropriately
adjusted within the range in which burning does not occur in the
ink or the like automatically or by manual operation of a user in
accordance with these conditions.
[0078] From the various viewpoints described above, it is
preferable to use the ink having the following features (i) to (iv)
as the ink having rapidly high viscosity evaporative drying
characteristics. When the ink having such features is used and
dried by irradiation with ultraviolet rays, for example, it is
possible to appropriately prevent the coffee stain phenomenon,
roughening of the ink, and smearing.
[0079] (i) 50% by weight or more of all solvents in the ink is a
liquid (such as water or an organic solvent) having a boiling point
of 100.degree. C. or more.
[0080] (ii) An ultraviolet absorber that absorbs ultraviolet rays
within a wavelength range of 300 nm to 490 nm is added to the ink.
In this case, the ultraviolet absorber absorbs ultraviolet rays,
thereby increasing the temperature of the solvent in the ink and
evaporating and drying the ink. The amount of the ultraviolet
absorber to be added is preferably 0.05% by weight or more and 20%
by weight or less based on the weight of all solvents. The
ultraviolet absorber may be either organic or inorganic.
[0081] (iii) The ink contains inorganic or organic coloring
materials, dispersants, various thickening substances, and the like
as necessary. As the thickening substance, additives which cause
rapid thickening action, such as various binder resins, rosin or
cellulose derivatives, acrylic acid derivatives, and thickening
agents such as polyvinyl alcohol, may be used. Further, as the
thickening substance, a resin (UV curable resin) polymerized by
ultraviolet curing (UV curing) to increase its viscosity may be
used, for example.
[0082] (iv) Rapid thickening to a viscosity of 50 mPasec or more
occurs with evaporation of at least 45% by volume or more of the
solvent of the initial solvent amount in the ink (expression of the
rapidly high viscosity evaporative drying characteristics). This
condition can be considered as a condition that viscosity increase
occurs rapidly at a stage where the solvent is larger than solvent
ink or the like in which the resin is dissolved in the solvent.
[0083] As for specific conditions and the like in the case of
printing in this embodiment, various modifications besides the
matters described above can be made. For example, the medium used
in this embodiment is not particularly limited. Also, the printing
speed, intended purposes, and the like are not particularly
limited. More specifically, in the case of using the instantaneous
drying ink as in this embodiment, for example, even when high-speed
printing is performed on a medium in which smearing is likely to
occur due to absorbability of paper, cloth, a sewn product such as
a T-shirt, or the like, occurrence of smearing during printing can
be appropriately prevented. Thus, in this embodiment, these media
can be suitably used. Not only when such an absorbent medium is
used, but also when a non-absorbent medium such as a vinyl chloride
sheet or various plastic films is used during printing, the effect
of preventing smearing by rapid drying and the like can be obtained
appropriately.
[0084] Specific configurations of the printing apparatus 10 can be
further variously modified. For example, the position where the
ultraviolet irradiation section is disposed can be variously
changed according to the configuration of the printing apparatus 10
and the like. In this case, for example, the ultraviolet
irradiation section may be installed at a position conforming to a
scanning type such as a serial type or a line type. In the case of
a line type configuration, for example, an ultraviolet irradiation
section may be individually disposed on the downstream side of an
inkjet head for each color of CMYK. Alternatively, an inkjet head
is disposed on the downstream side of a plurality of inkjet heads
for respective colors of CMYK, and ultraviolet rays may be applied
collectively to inks of the respective colors of CMYK.
[0085] The color of the ink to be used is not limited to the color
described above, but inks of various colors may be used. For
example, inks used as color inks are not limited to inks of process
colors such as CMYK, and, depending on the purpose of printing and
the like, inks of R (red), G (green), and B (blue) colors and other
special colors may be used. As the inks of special colors, in
addition to white color ink, metallic colored inks and
pearl-colored inks may be used, for example. Further, as the ink of
a special color, an ink of a clear color may be used, for example.
When ink of each color of RGB is used, each color of CMY can be
considered as a primary color, and each color of RGB can be
considered as a secondary color. In this case, the secondary color
is, for example, a color obtained by mixing a plurality of primary
colors in principle. In this case, the inkjet heads for secondary
colors may be arranged so as to be shifted in position in the sub
scanning direction from the inkjet heads for primary colors. With
this configuration, for example, it is possible to appropriately
reduce the total amount of ink to be ejected with respect to the
unit area in each main scan. Consequently, for example, occurrence
of smearing can be more appropriately suppressed, and highly
brilliant printing can be performed more appropriately. In this
case, it possible to more reliably prevent curling, cockling, and
the like from occurring even when using an absorbent medium or the
like, for example.
INDUSTRIAL APPLICABILITY
[0086] The present disclosure can be suitably used, for example, in
a printing apparatus.
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